Perception of Phantom Images and Music From Loudspeakers

In stereo playback, loudspeakers actually function as a phase-locked array of the first two early reflections of sound from the recorded space. From these two “early reflections” we would like to acquire a realistic, sense of the timbre, position and space of the recorded sound source and its environment.

Two loudspeakers alone, in an anechoic space, can’t do this very well. Instead of the rich multiplicity of sound artifacts that our ears desire and use for richer and more complete perception, we are constrained to two versions only of the recorded space. Also, it doesn’t help that all of the relative directional information of all the artifacts that our ears are equipped to detect has been lost at the microphones, which cannot detect such directional information.

Meanwhile, a key feature of stereophony is the existence of so-called “phantom images.” These images are illusions of sound emitting from points in space other than the loudspeakers. Interestingly, their existence confirms a breakdown in our auditory localization mechanism, because they incorrectly identify the location of sound sources (i.e. the sound does NOT appear to come from the loudspeakers, when in fact it DOES).

The whole story of phantom images is a little too complex for this article (again, take a look at Total Recording). As I’ve noted, the loudspeakers function as the first early reflections of a sound whose direct version was not emitted. Our auditory system infers the location of the sound source based on those “early reflections” from the two loudspeakers. Those perceived locations are the so-called phantom images. They are surprisingly life-like and real to us.